1. Field of the Invention
The present invention relate to a filter for use with a pulse wave sensor in determining a rising point of a pulse wave, and a pulse wave analyzing apparatus that determines a rising point of a pulse wave by analyzing the shape or form of the pulse wave.
2. Related Art Statement
A rising point of a pulse wave is identified or determined, for example, when a pulse wave propagation velocity at which the pulse wave propagates between two body portions of a living subject is measured, or when a pulse rate of the subject is measured. There is known a pulse wave sensor that is worn on a body portion of a living subject to detect a pulse wave from the body portion, and outputs a pulse wave signal representing the detected pulse wave. However, the pulse wave signal contains, in addition to components representing the pulse wave, low-frequency noise such as swell like DC component, or high-frequency noise such as artifact noise or background noise. Hence, a pulse wave filter is used to remove the noise and obtain a filtered pulse wave signal representing a desired pulse wave.
When the rising point of pulse wave is utilized, such a pulse wave filter is employed which has a specific frequency band covering frequencies of a rising portion of the pulse wave and allows the rising portion to pass therethrough. For example, a pulse wave filter disclosed by Japanese Patent Publication No. 2001-145606 has a specific frequency band of from 1 Hz to 30 Hz.
However, even in the case where the pulse wave filter that allows the rising portion of pulse wave to pass therethrough is employed and the pulse wave signal filtered by the filter is used to determine the rising point of pulse wave, the rising portion of the pulse wave represented by the filtered signal may not be so sharp as to be able to determine sufficiently accurately a time of detection or occurrence of the rising point.